As far as outsourcing, I have some info on how to communicate with the developer, not get ripped off, etc. But what about IP? Should I assume that any code that is outsourced has come from other projects and/or the code that I'm paying to have developed will be used by others in the future? Is there any way to control this (especially when dealing with a dev thru a computer screen)?

If you are supplying the developer with algorithms that are specific (critical/unique) to your business, then for the avoidance of doubt you should make explicit in the contract that you own the IP for any work the developer does for you.

It's unlikely that anyone would use a developer that they didn't know personally, without a formal contract, for this type of work though.

On the other hand, if you're asking for a vanilla e-commerce site then it's less relevant, the code the developer uses may come from open source libraries, or it may be his that he his re-using, but it probably matters little to you as it's the content on the site not the code behind it that you really care about.

You will always own the copyright on the website, including the design artefacts, unless you are explicitly licensing them.

Ideally you would also somehow get the developer to verify that all the code they are using has a valid licence, as ultimately you're probably liable for infringement. Again, I guess this is trickier to do in a web based developer market, but probably not going to be an issue for a vanilla job like an e-commerce site or marketplace.